Quenchable steel sheet having high hot press workability and method of manufacturing the same

Abstract

The quenchable steel sheet has an alloy composition including carbon (C) in an amount of 0.15˜0.30 wt %, silicon (Si) in an amount of 0.05˜0.5 wt %, manganese (Mn) in an amount of 1.0˜2.0 wt %, boron (B) in an amount of 0.0005˜0.0040 wt %, sulfur (S) in an amount of 0.003 wt % or less, phosphorus (P) in an amount of 0.012 wt % or less, one or more selected from among calcium (Ca) in an amount of 0.0010˜0.0040 wt % and copper (Cu) in an amount of 0.05˜1.0 wt %, two or more selected from among cobalt (Co), zirconium (Zr) and antimony (Sb), and iron (Fe). Alloy elements are controlled to increasing hot ductility and enabling pressing at 600˜900° C. so that a tensile strength of 1400 MPa or more and an elongation of 8% or more are obtained after pressing.

1. A steel sheet of a steel alloy composition comprising:
 iron (Fe); 
 carbon (C) in an amount of 0.15 to 0.30 wt %; 
 silicon (Si) in an amount of 0.05 to 0.5 wt %; 
 manganese (Mn) in an amount of 1.0 to 2.0 wt %; 
 boron (B) in an amount of 0.0005 to 0.0040 wt %; 
 sulfur (S) in an amount of 0.003 wt % or less; 
 phosphorus (P) in an amount of 0.012 wt % or less; 
 one or both of calcium (Ca) and copper (Cu), calcium being in an amount of 0.0010 to 0.0040 wt %, copper being in an amount of 0.05 to 1.0 wt % of copper (Cu); and 
 two or more selected from the group consisting of cobalt (Co), zirconium (Zr) and antimony (Sb), 
 wherein the cobalt (Co) and the antimony (Sb) are present in amounts to satisfy 0.0005 wt %≦(Co+Sb)≦0.5 wt %, 
 wherein the steel alloy composition does not comprise any one of Titanium (Ti), Niobium (Nb), Molybdenum (Mo) and Chromium (Cr). 
 
     
     
       2. The steel sheet of  claim 1 , wherein the zirconium (Zr) is present in an amount of 0.0005 to 0.1 wt %. 
     
     
       3. The steel sheet of  claim 1 , wherein a weight ratio of Ca/S is between 0.5 and 3.0. 
     
     
       4. The steel sheet of  claim 1 , wherein the alloy composition comprises antimony (Sb) in an amount of 0.02 to 0.5 wt %. 
     
     
       5. A steel sheet comprising:
 a first layer of a steel alloy composition which comprises iron (Fe) and at least one of cobalt (Co) and zirconium (Zr); and 
 a second layer comprising Al—Si and plated on the first layer, 
 wherein at least one of cobalt (Co) and Zirconium (Zr) is dispersed in the second layer, 
 wherein the steel alloy composition comprises:
 carbon in an amount of 0.15 to 0.30 wt %; 
 silicon (Si) in an amount of 0.05 to 0.5 wt %; 
 manganese (Mn) in an amount of 1.0 to 2.0 wt %; 
 boron (B) in an amount of 0.0005 to 0.0040 wt %; 
 sulfur (S) in an amount of 0.003 wt % or less; 
 phosphorus (P) in an amount of 0.012 wt % or less; and 
 one or both of calcium (Ca) and copper (Cu), calcium being in an amount of 0.0010 to 0.0040 wt %, copper being in an amount of 0.05 to 1.0 wt % of copper (Cu), 
 wherein the steel alloy composition does not comprise any one of Titanium (Ti), Niobium (Nb), Molybdenum (Mo) and Chromium (Cr). 
 
 
     
     
       6. The steel sheet of  claim 5 , wherein the second layer comprises a plurality of nuclei of the at least one of cobalt (Co) and Zirconium (Zr). 
     
     
       7. The steel sheet of  claim 5 , wherein the second layer has a thickness between 10 μm and 30 μm. 
     
     
       8. The steel sheet of  claim 5 , wherein the steel alloy composition comprises antimony (Sb) in an amount of 0.02 to 0.5 wt %.